Computing devices are increasingly embedded in objects and environments such as appliances, thermostats, books, furniture, and even implantable medical devices. A key issue is how to power these devices as they become smaller and numerous; wires are often not feasible, and batteries add weight, bulk, cost, and require recharging or replacement that adds costs and is difficult at large scales. Generating a conventional radio wave typically requires much more power than can be harvested from ambient RF signals. Traditional backscatter communication (e.g., RFID) provides a form of communicating by modulating reflections of an incident RF signal (e.g., rather than generating RF waves). Therefore, traditional backscatter transmission is orders of magnitude more energy-efficient than conventional radio communication. However, traditional backscatter communication requires deployment of a special purpose power infrastructure (e.g., an RFID reader) to transmit a high-power (1W) signal to nearby devices, which the nearby devices use to backscatter. Additionally, traditional RFID systems, RFID tags must talk exclusively to an RFID reader and are unable to even sense the transmissions of other RFID tags.